MATHS - Algebra - Quadratic Formula - Solving Quadratics

Quadratics can be solved in different ways: factorising, quadratic formula or by completing the square. In this video we are going to look at how to use the quadratic formula to solve quadratics. Quadratics can’t always be factorised, however the quadratic formula does always work. Factorising IS easier to do, so it’s better to check for that first. But if you can’t factorise, then we can use the quadratic formula instead. If the question says ‘giving your answer to 3 significant figures’ it means these quadratics cannot be factorised, so straight away look to use the quadratic formula. To solve quadratics, they always need to equal 0. So before you start, you may need to do some rearranging into the form ax2 + bx + c = 0. ‘a’ is the number in front of the x-squared, ‘b’ is the number in front of the ‘x’ and ‘c’ is the number on it’s own. Make sure you keep the sign in front of the numbers. We then just substitute these a,b and c values into the quadratic formula. You have to be very careful with negatives: it is best to use brackets. You will nearly always end up with 2 different answers, but occasionally you may get the same answer twice (which can still be correct).